[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Alternative formulations of keywords
Marc Feeley scripsit:
> If you try to formalize the cases in which it does work and the cases
> in which it doesn't you will realize that it is very hard to specify
> precisely. You have to assume a particular set of powerful analyzes
> that are performed by the compiler, and your semantics will depend on
> the existence of these analyzes. This places difficult constraints
> on the Scheme implementation.
It's syntactic sugar, so I'm fine with it not working in any case that's
at all tricky.
> For example can your proposed approach work in this case:
> (define (f g)
> (g foo: 11 bar: 22))
Plainly no. The compiler should cough with "keywords in call of unknown
> or in this case:
> (define (f #!key (x 11) (y 22)) (+ x y))
> (define (g z) (f y: z))
> (define (h) (set! f (lambda (#!key (y 33) (z 44)) (* y z))))
Again, plainly no. I might have said "only if the compiler can prove
that h is always called before g is", but that's precisely the sort
of tricky analysis neither of us would want to depend on.
Here the error is "keyword y: not known for function f."
In short, the definition of a function must be either global or
lexically apparent for it to be callable with keywords.
John Cowan http://ccil.org/~cowan firstname.lastname@example.org
Mr. Henry James writes fiction as if it were a painful duty. --Oscar Wilde